Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221938
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
238 PM CDT Mon Apr 22 2019

.SHORT TERM...(This evening through Tuesday)
Issued at 240 PM CDT Mon Apr 22 2019

This period has the most impact weather of the 7 days.
Temperatures will remain near or above normal through Friday.

At 19Z, surface low pressure was organizing across central Iowa on
the I-35 corridor north of Des Moines. Radar shows showers and
storms developing. Surface-based CAPE was growing in the warm
sector out ahead with mid-50s dewpoints. However, the moisture
was somewhat shallow and limited with MLCAPE much less. In the
next hours, MLCAPE will continue to grow with maybe 750 J/Kg
expected across the south by later afternoon. Probably a limiting
factor on severe weather.

At 19Z GOES Water Vapor imagery indicated broad cyclonic
rotation/shear over the region north of a zonal darkening band
across southern Iowa. This darkening represented the polar jet
axis pretty well with the mid-level wind max slightly more SW-NE,
and the 18Z DVN RAOB shows 45-50 kts at 500 mb, also verified by
the radar VWP. This wind max provides supercell shear over the
warm sector ahead of the low pressure area, northward to about
the WI/IL border. Thus, most of the forecast area is under a
pulse or multicell shear profile.

Storms will continue to develop, in a weakly capped environment,
as the afternoon continues and mainly south and east of La Crosse,
through the evening. Some of the CAM solutions suggest a line of
storms may form across the south by later afternoon which seems
reasonable given 0-3km shear of 30-35 kts. Some supercell
structures are possible Fayette, Clayton and Grant co. 0-1km
shear is generally unfavorable so any tornado activity would
likely be brief and weak. Plus, 19Z surface observations show the
flow is veered in the warm sector and less favorable under the
mid- level wind max. Bottom line is storms with lightning and 0.50
to 1" of rain south and east of La Crosse mainly. There could be
isolated 1-2" rain amounts, if a focus is created such as a
deformation area north of the low. Feeling like the deformation
zone will form, but location is difficult to place - possibly a
CCY-LSE-ISW line? Isolated damaging wind gusts cannot not be ruled
out across Fayette-Clayton-Grant counties.

This rainfall may aggravate ongoing flooding and high rivers.
Confidence isnt high enough for a flood watch for river rises,
but should certain basins /like the Kickapoo/ see 1-2", flooding
is probable.

The rain will be ending from west to east in the later evening and
after midnight.

.LONG TERM...(Tuesday night through Monday)
Issued at 240 PM CDT Mon Apr 22 2019

A quiet weather week with some rain chances Wednesday night and
Thursday with a weaker frontal/trough passage.

The weekend is really a mess right now in the predictability
area. Enormous spread is in the medium range guidance on how
Saturday will evolve. It appears as though the solution spread
will still bring higher rain chances to the area, but the duration
and timing are very different. Saturday`s highs in the guidance
range from the 40s to 60s. Went with a blend of the solutions for
now.
&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1222 PM CDT Mon Apr 22 2019

Aviation conditions will depend on what side of this passing short
wave you are on.

Ahead of it lots of VFR ceilings with embedded convection. With warm
front working into southern areas, could see occasional breaks, but
expect more thunderstorms with local visibility restrictions to
reform given lift ahead of wave and higher dew points.

Meanwhile north and west of the wave, already seeing winds shift to
north or northeast, and this is where IFR ceilings will begin to
push in. As wave exists, stratus deck will sweep in this evening and
last into Tuesday morning.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Baumgardt
LONG TERM...Baumgardt
AVIATION...Shea


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